#pragma once

// Float32 to float16 compressor
// Code from here: https://stackoverflow.com/a/3542975
// Used under the Unlicense: http://choosealicense.com/licenses/unlicense/

class Float16Compressor
{
    union Bits
    {
        float f;
        int32_t si;
        uint32_t ui;
    };

    static int const shift = 13;
    static int const shiftSign = 16;

    static int32_t const infN = 0x7F800000; // flt32 infinity
    static int32_t const maxN = 0x477FE000; // max flt16 normal as a flt32
    static int32_t const minN = 0x38800000; // min flt16 normal as a flt32
    static int32_t const signN = 0x80000000; // flt32 sign bit

    static int32_t const infC = infN >> shift;
    static int32_t const nanN = (infC + 1) << shift; // minimum flt16 nan as a flt32
    static int32_t const maxC = maxN >> shift;
    static int32_t const minC = minN >> shift;
    static int32_t const signC = signN >> shiftSign; // flt16 sign bit

    static int32_t const mulN = 0x52000000; // (1 << 23) / minN
    static int32_t const mulC = 0x33800000; // minN / (1 << (23 - shift))

    static int32_t const subC = 0x003FF; // max flt32 subnormal down shifted
    static int32_t const norC = 0x00400; // min flt32 normal down shifted

    static int32_t const maxD = infC - maxC - 1;
    static int32_t const minD = minC - subC - 1;

public:

    static uint16_t compress(float value)
    {
        Bits v, s;
        v.f = value;
        uint32_t sign = v.si & signN;
        v.si ^= sign;
        sign >>= shiftSign; // logical shift
        s.si = mulN;
        s.si = static_cast<int32_t>(s.f * v.f); // correct subnormals
        v.si ^= (s.si ^ v.si) & -(minN > v.si);
        v.si ^= (infN ^ v.si) & -((infN > v.si) & (v.si > maxN));
        v.si ^= (nanN ^ v.si) & -((nanN > v.si) & (v.si > infN));
        v.ui >>= shift; // logical shift
        v.si ^= ((v.si - maxD) ^ v.si) & -(v.si > maxC);
        v.si ^= ((v.si - minD) ^ v.si) & -(v.si > subC);
        return static_cast<uint16_t>(v.ui | sign);
    }

    static float decompress(uint16_t value)
    {
        Bits v;
        v.ui = value;
        int32_t sign = v.si & signC;
        v.si ^= sign;
        sign <<= shiftSign;
        v.si ^= ((v.si + minD) ^ v.si) & -(v.si > subC);
        v.si ^= ((v.si + maxD) ^ v.si) & -(v.si > maxC);
        Bits s;
        s.si = mulC;
        s.f *= v.si;
        int32_t mask = -(norC > v.si);
        v.si <<= shift;
        v.si ^= (s.si ^ v.si) & mask;
        v.si |= sign;
        return v.f;
    }
};